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Abstract:

A vehicle roof window includes an uncoated glass transparency having an
Lta in the range of greater than 0% to 10%, and a solar factor in the
range of equal to or less than 30%, measured at a thickness in the range
of 3.6-4.1 millimeters (`mm"), e.g. at a thickness of 3.6 mm, 3.9 mm or
4.1 mm. The solar factor is determined in accordance to International
Organization for Standardization ("ISO") No. 13837.

Claims:

1. A glass comprising: a base soda-lime-silica glass portion, and a
colorant portion, wherein the colorant portion provides the glass with a
solar factor of equal to or less than 30% at a glass thickness in the
range of 3.6 to 4.1 millimeters ("mm"), wherein the solar factor is
calculated in accordance to the International Organization for
Standardization No. 13837.

2. The glass according to claim 1, wherein the glass has a first major
surface and an opposite second major surface, and a first set of
properties of the glass and assigned values to the first set of
properties to determine the solar factor of the glass in accordance with
the International Organization for Standardization No. 13837 comprise:
TABLE-US-00009
emissivity of the first surface 0.837,
emissivity of the second surface 0.837,
wind speed 4 meters per second,
heat transfer coefficient of the first surface 21 watts/square
meter Kelvin,
heat transfer coefficient of the second surface 8 watts/square
meter Kelvin
glass thickness 3.6-4.1 mm, and

a second set of properties of the glass to determine the solar factor of
the glass in accordance with the International Organization for
Standardization No. 13837 comprise: total solar energy transmittance
("TSET"); total solar energy reflected ("TSER"), and total solar energy
absorbed ("TSEA"), wherein the TSET, TSER and TSEA are determined at a
glass thickness in the range of 3.6-4.1 3.9 mm.

3. The glass according to claim 2, wherein the glass is a window for a
land, air, space, on the water and under the water vehicle; for
residential and commercial structures, and for residential and commercial
doors, oven doors and see through refrigerator doors.

4. The glass according to claim 3, wherein the window is a roof window
for a vehicle, and the glass is tempered or heat strengthened.

5. The glass according to claim 1 wherein the glass has a visible light
transmission [2 degree observer] ("Lta") (C.I.E. illuminant A) of greater
than 0% and equal to or less than 15% at a glass thickness of 3.9 mm and
in a wavelength range of greater than 380 nm to less than 780 nm.

6. The glass according to claim 5 wherein the visible light transmission
is in the range of greater than 0% to 10%.

7. The glass according to claim 6 wherein the visible light transmission
is in the range of greater than 0% to 3%.

9. The glass according to claim 2 wherein the colorant portion,
comprises:
TABLE-US-00011
total iron as Fe2O3 equal to or greater than 0.950 weight
percent;
FeO equal to or greater than 0.50 weigh percent;
CoO greater than 0.030 weight percent;
Redox ratio equal to or greater than 0.50.

10. The glass according to claim 2, wherein the glass has a TSET of
greater than 0% and equal to or less than 5%, a TSER of greater than 3%
and equal to or less than 7%, and a TSEA of greater than 90% and equal to
or less than 97%, and selected ones of the TSET, TSER, and TSEA are
measured over a wavelength of 300 to 2500 nm at a glass thickness of 3.9
mm.

11. The glass according to claim 10 wherein the glass has a TSET of
greater than 1% and equal to or less than 5%, a TSER of greater than 3%
and equal to or less than 5%, and a TSEA of greater than 92% and equal to
or less than 95%.

12. The glass according to claim 10, wherein the window is a roof window
for a vehicle. wherein the glass has a visible light transmission [2
degree observer] ("Lta") (C.I.E. illuminant A) of greater than 0% and
equal to or less than 15% at a glass thickness of 3.9 mm and in a
wavelength range of greater than 380 nm to less than 780 nm. wherein the
base soda-lime-silica glass portion, comprises
TABLE-US-00012
SiO2 66-75 weight percent;
Na2O 10-20 weight percent;
CaO 5-15 weight percent;
MgO 0-5 weight percent;
Al2O3 0-5 weight percent;
K2O 0-3 weight percent, and
BaO 0-1 weight percent,

wherein the colorant portion, comprises:
TABLE-US-00013
total iron as Fe2O3 equal to or greater than 0.950 weight
percent;
FeO equal to or greater than 0.50 weight percent;
CoO greater than 0.030 weight percent;
Redox ratio equal to or greater than 0.50.

13. The glass according to claim 10, wherein the TSET and TSER are
measured over a wavelength of 300 to 2500 nm at a glass thickness of 3.9
mm and the TSEA is determined by subtracting the values of the measured
TSET and TSER from 100%.

14. The glass according to claim 2 wherein the colorant portion,
comprises:
TABLE-US-00014
total iron as Fe2O3 in the range of 0.900 to 1.3 weight
percent;
FeO in the range of 0.50-0.900 weight percent;
CoO greater than 0.030 weight percent;
Redox ratio equal to or greater than 0.50-0.850.

15. The glass according to claim 13 comprising sulfur expressed as
SO3 in the range of 0.04 to 0.10 weight percent.

16. The glass according to claim 1 wherein the thickness is 3.6 mm.

17. The glass according to claim 1 wherein the thickness is 4.1 mm.

18. The glass according to claim 1 wherein the thickness is 3.9 mm.

19. The glass according to claim 2 wherein the thickness of the first set
of properties and the thickness of the second set of properties is 3.9
mm.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a dark privacy glass having a low solar
factor, and more particularly, to vehicle windows, e.g. automotive roof
windows made using the dark privacy glass, the windows having a solar
factor equal to or below 30% calculated in accordance to the
International Organization for Standardization ("ISO") No.13837.

[0003] 2. Discussion of the Technical Challenge

[0004] There is continued interest in reducing the load applied to vehicle
engines, e.g. automotive gasoline engines to increase the miles per
gallon of gasoline and to reduce the carbon monoxide exhausted from the
engines. Of particular interest in the present discussion are the imposed
and the proposed regulations of the Federal Clean Air Act and of the
California Air Resources Board ("CARB") directed to vehicle windows, e.g.
automotive windows to reduce solar energy passing through the windows to
reduce solar heating of the vehicle interior. As is appreciated by those
skilled in the art, reducing solar heating of the vehicle interior,
especially during the summer months reduces the air conditioner load on
the engine. The proposed CARB regulation includes regulations directed to
the automotive roof window and requires that the transparency of the roof
window, e.g. the glass transparency have a solar factor of a specified
value determined according to International Organization for
Standardization ("ISO") No,13837. As is appreciated by those skilled in
the art, the automotive roof window can be securely mounted in the roof
or can be mounted in the roof for reciprocating movement between an open
position and a closed position. Further automotive roof windows are also
referred to as sun windows and moon windows.

[0005] The solar factor is a measure of the percent of solar energy or
heat that passes through the glass transparency, e.g. the roof window
into the car interior. The lower the solar factor, the higher the solar
protection and the higher the performance of the glass transparency in
preventing passage of solar energy into the vehicle interior. Using a
solar control glass transparency can reduce the need for
air-conditioning, thereby reducing air pollution and increasing miles per
gallon of fuel.

[0006] The formula for calculating the solar factor recited in ISO No.
13837 includes the following variables: total solar energy transmission
of the transparency; total solar energy reflectance of the transparency;
total solar energy absorbance of the transparency, emissivity of the
surfaces of the transparency facing the interior and exterior of the
vehicle, speed of the wind moving over the exterior surface of the
transparency, thickness of the transparency and heat transfer coefficient
of the interior and the exterior surfaces of the transparency. A
government, state or municipal agency selects the value of the solar
factor. By way of illustration and of interest to the present discussion,
CARB has selected a solar factor for transparencies for roof windows of
equal to or less than 30%.

[0007] As can be appreciated by those skilled in the art, it would be
commercially advantageous to provide glass transparencies for vehicle
roof windows that meet the solar factor requirement set by the
government, state and/or municipal agencies, e.g. but not limiting to the
solar factor set by CARB.

SUMMARY OF THE INVENTION

[0008] The invention relates to a glass, e.g. a dark privacy glass,
including, among other things, a base soda-lime-silica glass portion, and
a colorant portion. The colorant portion provides the glass with a solar
factor of equal to or less than 30% at a glass thickness in the range of
3.6-4.1 millimeters, wherein the solar factor is calculated in accordance
to the International Organization for Standardization No. 13837.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is plan view of an automobile showing a roof window
incorporating features of the invention.

[0010] FIG. 2 is a view of non-limiting embodiments of a glass
transparency incorporating features of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] As used herein, unless otherwise expressly specified, all numbers
such as those expressing values, ranges, amounts or percentages are read
as if prefaced by the word "about", even if the term does not expressly
appear. When referring to any numerical range of values, such ranges are
understood to include each and every number and/or fraction between the
stated range minimum and maximum. For example, a range of "1 to 10" is
intended to include all sub-ranges between and including the recited
minimum value of 1 and the recited maximum value of 10, that is, having a
minimum value equal to or greater than 1 and a maximum value of equal to
or less than 10. As employed herein, the term "number" means one or an
integer greater than one.

[0012] Before discussing non-limiting embodiments of the invention, it is
understood that the invention is not limited in its application to the
details of the particular non-limiting embodiments shown and discussed
herein since the invention is capable of other embodiments. Further, the
terminology used herein to discuss the invention is for the purpose of
description and is not of limitation. Still further, unless indicated
otherwise, in the following discussion like numbers refer to like
elements.

[0013] The non-limiting embodiments of the invention discussed herein are
directed to an automobile roof window having a solar control glass
transparency; the invention, however, is not limited thereto. More
particularly, the glass transparency can be a part of a window for any
type of land, air, space, on the water and under the water vehicle; of
any residential or commercial window, and of windows for residential and
commercial doors, oven doors and see through refrigerator doors. In
addition, the automotive window is not limited to a roof window but can
be a vehicle back, or side window. Still further, the roof window is not
limited to any particular design and any of the stationary and moveable
roof window designs can be used in the practice of the invention

[0014] With reference to FIGS. 1 and 2 as needed, roof 10 of automobile 12
has a roof window 14 that includes a glass transparency or glass
substrate 16. The transparency 16 has a major surface 20 facing the
automobile exterior and an opposite major surface 24 facing the
automobile interior. The transparency can be securely mounted in the roof
for no movement, or mounted in the roof for reciprocating movement
between a closed position and an open position. For a discussion of
securing a window in a vehicle, reference can be made to U.S. Patent
Publication No. U.S. 2007/0079564A1, and for a discussion of a moveably
mounting a roof window in a vehicle, reference can be made to U.S. Patent
Publication No. U.S. 2008/0081148A1, which documents in their entirety,
is hereby incorporated by reference.

[0015] At the present time, the solar factor for roof windows proposed by
CARB is not adopted and is not mandatory; nevertheless, for a full
appreciation of the non-limiting embodiments of the invention, glass
transparencies meeting the solar factor for roof windows proposed by CARB
will be discussed. The solar factor is equal to or less than 30%
calculated in accordance to ISO No. 13837, which document in its entirety
is hereby incorporated by reference. Properties of the glass transparency
that are used to determine the solar factor include the following: total
solar energy transmission (hereinafter also referred to as "TSET") of the
glass transparency; total solar energy reflectance (hereinafter also
referred to as "TSER`) of the glass transparency; total solar energy
absorbance (hereinafter also referred to as "TSEA") of the glass
transparency, emissivity of the exterior surface 20, and of the interior
surface 24, of the glass transparency 16 (see FIG. 2), speed of the wind
moving over the exterior surface of the glass transparency, thickness of
the glass transparency and heat transfer coefficient of the exterior
surface 20 and the interior surface 24 of the glass transparency 16.

[0016] For purposes of discussion and not limiting to the invention, in
one non-limiting embodiment of the invention, the transparency 16 is a
glass transparency or glass substrate and the emissivity of the exterior
surface 20 and of the interior surface 24 of the substrate 16 is the same
value, and the value of the emissivity is 0.837. The wind speed is 4
meters per second, which is the wind speed of the vehicle at rest as
recited in ISO 13837. At 4 meters per second, the heat transfer
coefficient of the exterior surface 20 of the substrate 16 is 21
watts/square meter Kelvin and of the interior surface 24 of the substrate
16 is 8 watts/square meter Kelvin. The thickness of the glass substrate
16 is in the range of 3.6-4.1 millimeters ("mm"). In the following
discussions of the properties of the non-limiting embodiments of the
glasses of the invention, the referenced thickness is 3.9 mm; however,
the properties of the non-limiting embodiment of the glasses of the
invention can be found in the thickness range of 3.6-4.1 mm. As can be
appreciated the invention is not limited to the values set forth for
emissivity, wind speed, thickness and heat transfer coefficients, and the
values are used with the values of the TSET, TSER, TSEA and solar factor
to define the performance of the glass transparency or glass substrate 16
of the invention.

[0017] The remaining parameters for determining the solar factor in
accordance to ISO 13837, namely TSET, TSER and TSEA, are measured over
the wavelength range of 300 to 2500 nanometers ("nm") at a glass
transparency thickness of 3.9 mm, For purposes of clarity, the
ultraviolet wavelengths are less than 380 nm, the visible wavelengths are
in the range of equal to or greater than 380 nm to less than 780 nm, and
the infrared wavelengths are equal to or greater than 780 nm. As can be
appreciated by those skilled in the art TSET, TSER and TSEA can be
measured, or two of the group measured and the third calculated from one
of following equations (1)-(3):

TSET=100%-TSER-TSEA; (1)

TSER=100%-TSEA-TSET; (2)

TSEA=100%-TSET-TSER, (3)

[0018] where TSET, TSER and TSEA are as defined herein.

[0019] TSET is the ratio or percent of total solar energy transmitted
through the glass transparency 16 to the amount of total solar energy
incident or falling on the exterior surface 20 of the transparency 16.
The TSET data provided throughout this disclosure is based on a glass
thickness of 3.9 millimeters (0.1535 inch). Total solar energy
transmittance (TSET) represents a computed value based on measured
transmittances from 300 to 2500 nm at 5 nm, 10 nm, and 50 nm intervals
for the UV, visible and IR wavelengths. The transmittance data is
calculated using ASTM air mass 1.5 direct solar irradiance data and
integrated using the trapezoidal rule, as is known in the art, e.g. as
discussed in U.S. Pat. No. 5,393,593, which patent in its entirety is
hereby incorporated by reference. In the practice of the invention, the
glass transparency 16 at a thickness of 3.9 mm preferably has a TSET of
greater than 0% and equal to or less than 5%, and more preferably from 1%
to 5%.

[0020] The TSER is the ratio or percent of the amount of the total solar
energy directly reflected by the exterior surface 20 of the glass
transparency 16 and by the interior or second surface 24 of the glass
transparency 16 to the amount of total solar energy incident on the
exterior surface 20 of the glass transparency 16. As is appreciated by
those skilled in the art, the solar energy reflected from the interior or
second surface 24 is the solar energy that passes through the exterior
surface 24, does not pass through the interior or second surface 24 but
is reflected by the interior or second surface 24 toward the exterior
surface 20 and passes through the exterior surface 20. For a more
detailed discussion of solar rays incident on glass surfaces, reference
can be made to U.S. patent application Ser. No. 12/911,189 filed Oct. 25,
2010 in the name of Benjamin Kabagambe et al and titled "Electrocurtain
Coating Process for Solar Mirrors", which document in its entirety is
hereby incorporated by reference.

[0021] In the practice of the invention the TSER of the glass transparency
is measured over the wavelength range of 300 to 2500 nm of the
electromagnetic scale at a glass thickness of 3.9 mm (0.1535 inches). The
reflectance data is calculated using ASTM air mass 1.5 direct solar
irradiance data and integrated using the trapezoidal rule, as is known in
the art. In the practice of the invention, the glass transparency or
glass substrate 16 at a thickness of 3.9 mm preferably has a TSER of
greater than 3% and equal to or less than 7%, and more preferably from 3%
to 5%.

[0022] The TSEA is the ratio or percent of the amount of the total solar
energy directly absorbed by the glass transparency 16 to the amount of
total solar energy incident on the exterior surface 20 of the
transparency 16. In the non-limiting embodiment of the invention under
discussion and for purposes of defining the non-limiting embodiment of
the invention under discussion, the TSET and TSER of the glass
transparency 16 are measured as discussed above, or in any other usual
manner, and the TSEA is calculated using equation (3) above. In the
practice of the invention, the glass transparency 16 at a thickness of
3.9 mm preferably has a TSEA of greater than 90% and equal to or less
than 97%, and more preferably from 92% to 95%.

[0023] Reducing the TSET reduces the transmission of solar energy through
the glass transparency 16 into the automotive interior, which reduces the
transmission of visible light and invisible light into the automotive
interior and visa versa. Increasing the TSER increases the reflection of
solar energy from the surface 20 of the transparency 16, which reduces
the transmission of solar energy, e.g. visible light and invisible light
through the transparency 16 into the automotive interior and visa versa.
Increasing the TSEA decreases the transmission of solar energy, e.g.
visible light and invisible light into the automotive interior and visa
versa. As can be appreciated, increasing one of TSET, TSER or TSEA
effects the remaining ones of TSET, TSER and TSEA in accordance to above
equations (1)-(3).

[0024] The reduction of invisible light, e.g. ultraviolet solar energy and
infrared solar energy passing through the glass transparency into the
automotive interior is acceptable, however, reduction of visible light
into the automotive interior reduces the advantage of having a roof
window 14 (see FIG. 1). Although not a required property of the glass
transparency to determine the solar factor pursuant to ISO 13837, in the
practice of the invention, but not limiting to the invention, the glass
transparency 16 at a thickness of 3.9 mm, preferably has a luminous or
visible light transmission [2 degree observer] ("Lta") (C.I.E. illuminant
A) of greater than 0% and equal to or less than 15%; and more preferably
in one or more of the following ranges: greater than 0% to 10%; greater
than 0% to 6%; greater than 0% to 5%; greater than 0% to 4%; greater than
0% to 3%; greater than 0% to 2%; greater than 0% to 1%; 1% to 10%; 1% to
6%; 1% to 5%; 1% to 4%; 1% to 3%, and 1% to 2%.

[0025] It is noted that luminous transmittance [2 degree observer] ("Lta")
(C.I.E. illuminant A) is understood in the art, and is used herein in
accordance with its known meaning. This term is also known as "Ill. A"
visible transmittance and is in the range of equal to or greater than 380
to less than 780 nm, and its measurements are made in accordance with CIE
Publication 15.2 (1986) and ASTM E308. The transmittance data provided
throughout this disclosure is based on a glass thickness of 3.9
millimeters (0.1535 inch). Luminous transmittance (Lta) is measured using
C.I.E. 1931 standard illuminant "A" over the wavelength range equal to or
greater than 380 to 780 nanometers at 10 nanometer intervals.

[0026] In the following discussion, unless indicated otherwise the solar
factor for glasses of the invention used for glass transparencies is
determined according to ISO 13837, using an emissivity of 0.837 for the
exterior surface 20, and 0.837 for the interior surface 24, of the glass
transparency or glass substrate 16; a wind speed of 4 meters per second
over the exterior surface 20 of the glass transparency; a heat transfer
coefficient of 21 watts/square meter Kelvin for the exterior surface 20,
and a heat transfer coefficient of 8 watts/square meter Kelvin for the
interior surface 24, of the glass transparency 16; a glass transparency
thickness of 3.9 mm; a measured TSET and TSER, and a TSEA calculated
using Equation (3) above.

[0027] In the practice of the invention glasses for the glass transparency
16 are soda-lime-silicate glasses having a base glass portion and a
colorant portion. In general and not limiting to the invention, the base
glass portion includes, but is not limited to:

TABLE-US-00002
total iron as Fe2O3 equal to or greater than 0.950 weight
percent;
FeO equal to or greater than 0.50 weight percent;
CoO greater than 0.030 weight percent;
Redox ratio equal to or greater than 0.50.

[0028] Any reference to composition amounts, such as "weight percent", "wt
%" or "wt. %", "parts per million" and "ppm" are based on the total
weight of the final glass composition, or the total weight of the mixed
ingredients, e.g. but not limited to the glass batch materials, which
ever the case may be. The "total iron" content of the glass compositions
disclosed herein is expressed in terms of Fe2O3 in accordance
with standard analytical practice, regardless of the form actually
present. Likewise, the amount of iron in the ferrous state (Fe++) is
reported as FeO, even though it may not actually be present in the glass
as FeO. The proportion of the total iron in the ferrous state is used as
a measure of the redox state of the glass and is expressed as the ratio
FeO/Fe2O3, which is the weight percent of iron in the ferrous
state (expressed as FeO) divided by the weight percent of total iron
(expressed as Fe2O3). The total amount of iron present in the
glass is expressed herein in terms of Fe2O3 in accordance with
standard analytical practice, but that does not imply that all of the
iron is actually in the form of Fe2O3. Unless stated otherwise,
the term Fe2O3 in this specification shall mean total iron
expressed in terms of Fe2O3 and the term FeO shall mean iron in
the ferrous state expressed in terms of FeO.

[0029] Significant characteristics of the glass of the present invention
are relatively high total iron concentration (above 0.950 weight percent)
and FeO concentrations in the glass of at least 0.50 weight percent, in
some cases up to 0.90 weight percent, and in the most preferred examples
between 0.50 to 0.875 weight percent. High total iron reduces luminous
transmittance, and high ferrous iron is particularly helpful in reducing
infrared transmittance. Melting glass with large amounts of iron is
difficult due to poor heat transfer. As a result, when total iron is
greater than 1.0 weight percent, generally additional melting
enhancements must be provided to insure proper melting, e.g. bubblers and
electrodes.

[0030] Melting and refining aids such as SO3, fluorine, chlorine, and
lithium compounds are sometimes used, and small amounts can be detected
in this type of glass. To this base glass are added the coloring
constituents of the present invention set forth above. The glass is
essentially free of nickel; that is, no deliberate addition of nickel or
nickel compounds is made, although the possibility of traces of nickel
due to contamination may not always be avoided. Likewise, the glass is
essentially free of colorants other than iron and cobalt, and
specifically it is essentially free of chromium, titanium, and manganese
other than any trace amounts that may be present as impurities. More
particularly, amounts of chromium below 0.001 weight percent ("wt %");
amounts of titanium below 0.02 wt % and manganese below 0.003 wt %; are
considered trace amounts. Accordingly, the glass of the present invention
can be melted and refined in a continuous, large-scale, commercial
melting furnace and formed into flat glass sheets of varying thicknesses
by the float method in which the molten glass is supported on a pool of
molten metal, usually tin, as it assumes a ribbon shape and is cooled.

[0031] To avoid requiring unduly large amounts of total iron to meet the
objectives of the present invention it is useful to enhance the
proportion of iron in the ferrous state. Attaining the ferrous iron
levels of the present invention requires controlling the redox conditions
during melting so that conditions are relatively reducing. The redox
ratio for the glass of the present invention can be maintained at 0.50 to
about 0.850, for example, when the total iron concentration is in the
preferred concentrations (0.900 to 1.3 wt %). Redox ratios above 0.50 can
result in the formation of iron or ferric sulfide, which gives the glass
amber coloration. In the preferred practice of the invention, but not
limiting to the invention, sulfur expressed as SO3 in the range of
0.04 to 0.10 wt % is preferred, and in the range of 0.05 to 0.09 wt % is
more preferred, to enhance the formation of the ferric sulfide complex.

[0032] As is appreciated by those skilled in the art redox control is
achieved by means of controlling process conditions during the
glassmaking process, e.g. using reducing agents such as coal, sugar or
hydrocarbon fuel sprayed on batch materials, and increasing movement of
the molten glass using stirrers and/or bubblers. Because redox control is
well known in the art, no further discuss regarding redox control is
deemed necessary. For additional discussions regarding redox control
reference can be made to U.S. Pat. Nos. 5,393,593 and 6,673,730, which
patents in their entirety are hereby incorporated by reference.

[0033] The colorant cobalt produces a blue color, and the colorant iron
contributes yellow and blue in varying proportions depending upon the
oxidation state. The colorant iron in the ferric state (Fe2O3)
produces a yellow color in transmission and the colorant iron in the
ferrous state (FeO) produces a blue color in transmittance. Relatively
high concentrations of CoO in this glass help to produce low luminous
transmittance and a low TSET.

[0034] The glass compositions disclosed in the present invention can be
made using any of several types of melting arrangements, such as but not
limited to, a conventional, overhead fired continuous melting operation
as is well known in the art as the Siemens' process or a multi-stage
melting operation as disclosed in U.S. Pat. No. 4,792,536 (Pecoraro et
al.), which patent in its entirety, is hereby incorporated by reference.

[0035] Conventional, overhead fired continuous melting operations
(Siemens' process) are characterized by depositing batch material onto a
pool of molten glass maintained within a tank type melting furnace and
applying thermal energy until the materials are melted into the pool of
molten glass. The melting tanks conventionally contain a large volume of
molten glass so as to provide sufficient residence time for currents in
the molten glass to affect some degree of homogenization and fining
before the glass is discharged into a forming operation. One such
operation used for producing glass of the present invention incorporates
a refiner and conditioner arrangement as disclosed in U.S. Pat. No.
4,798,616 to Knavish et al., which patent in its entirety, is hereby
incorporated by reference. In addition, the waist area includes a waist
cooler and a pair of submerged coolers positioned upstream and downstream
from a set of stirrers.

[0036] Another glass melting and refining operation is disclosed in U.S.
Pat. Nos. 4,792,536 and 4,381,934, which patents in their entirety are
hereby incorporated by reference. The overall melting process disclosed
in U.S. Pat. No. 4,792,536 is characterized by separate stages whereby
more flexibility in controlling redox conditions is provided. The three
stages include a liquefaction stage, a dissolving stage, and a vacuum
refining stage. For a discussion of the three stages, reference can be
made to the above-identified patents.

[0037] Typically, flat glass batch includes sodium sulfate as a melting
and refining aid in the amounts of about 5 to 15 parts by weight per 1000
parts by weight of the silica source material (sand), with about 10 parts
by weight considered desirable to assure adequate refining.
Soda-lime-silica glass products, particularly flat glass products that
are mass-produced by conventional continuous melting processes are
characterized by significant amounts of residual refining aids. In such
products, the residual sulfur content (expressed as SO3) is
typically on the order of 0.2% by weight and seldom less than 0.1% by
weight. Even when no deliberate addition of sulfur refining aid is made
to the batch, at least 0.02% by weight SO3 is usually detected in a
soda-lime-silica glass made in a conventional continuous melter. In
distinction thereto, soda-lime-silica glass made in accordance with U.S.
Pat. No. 4,792,536 can be produced continuously by the embodiment
disclosed in the reference patents with less than 0.02% by weight
residual SO3, even when relatively small amounts of sulfur refining
aid are being included in the batch as described above, and less than
0.01% by weight SO3 when no deliberate inclusion of sulfur is being
made.

[0038] Although not limited thereto, the glass of the present invention
will most commonly be embodied by a flat sheet suitable for glazing
windows of vehicles or buildings. Usually the sheet form will be made by
the float process. A sheet of glass that has been formed by the float
process (i.e., floated on molten tin) is characterized by measurable
amounts of tin oxide that have migrated into surface portions of the
glass on at least one side. Typically, a piece of float glass has a
SnO2 concentration of at least 0.05 wt % in the first few microns
below the surface that was in contact with the tin. In the practice of
the invention, any differences between the emissivity and the heat
transfer coefficient of the exterior surface 20 and the interior surface
24 as a result of the tin oxide migrating into the surface of the glass
is ignored. More particularly, regardless of the air side of the glass
facing the interior or the exterior of the vehicle, the value of the
emissivity of the exterior surface of the glass and the emissivity of the
interior surface of the glass in determining the solar factor pursuant to
ISO 13837 is 0.837. The heat transfer coefficient in determining the
solar factor pursuant to ISO 13837 of the exterior surface 20 is 21
watts/square meter Kelvin and the heat transfer coefficient of the
interior surface is 8 watts/square meter Kelvin.

[0039] Twelve (12) Examples of glass compositions at a 3.9 mm (0.1535 in.)
reference thickness which embody the principles of the present invention
were made in the following manner.

[0040] Each of the twelve melts included the raw materials (basic batch
mixture) listed in Table 1. To prepare the melts, the raw materials at
the parts by weight listed in Table 1 were mixed to produce an Example
having a final glass weight of approximately 500 grams.

Rouge and Co3O4 were added as required for each example to
control the glass transmission within the preferred ranges. The amount of
rouge was 5.25 to 5.55 parts by wt. The amount of Co3O4 was
0.1875 parts by wt. Sulfur was added in the form of salt cake, which has
the chemical formula Na2SO4. Coal was added to each melt in
various amounts as needed to control glass redox.

[0041] A portion of about half of the raw batch material was placed in a
silica crucible in an electric furnace and heated to 2450° F.
(1343° C.) for 30 minutes. The molten batch was then heated and
held at 2500° F. (1371° C.) for 30 minutes. When the batch
material melted, the remaining raw materials were added to the crucible.
The molten batch was then heated to 2550° F. (1399° C.) for
30 minutes and 2600° F. (1427° C.) for 60 minutes. Next,
the molten glass was fritted in water, dried and reheated to 2650°
F. (1454° C.) for two hours. The molten glass was then poured out
of the crucible to form a slab and annealed. Samples were cut from the
slab and ground and polished for analysis.

[0042] The major ingredients and ranges of the ingredients of the base
glass composition for Examples 1-12 are listed in TABLE 2.

[0044] Small amounts of these melting and refining aids and tramp
materials, usually less than 0.3 wt %, may be present in the glass
compositions of the present invention without effect on the properties.

[0045] The chemical analysis of the glass compositions of Examples 1-12
was determined by x-ray fluorescence spectroscopy. The spectral
characteristics of the glass were determined on annealed samples using a
Perkin-Elmer Lambda 9 UV/VIS/NIR spectrophotometer. The FeO content was
determined from the transmittance at 1000 nm. The total iron (as
Fe2O3) was determined by x-ray fluorescence. The redox ratio
was then calculated as the spectral FeO divided by the total iron (as
Fe2O3).

[0046] The colorants and ranges of wt % of examples 1-12 are listed in the
following TABLE 4:

[0047] The color properties for Examples 1-12 are listed in TABLE 5. The
measurements were made at a glass thickness of 3.9 mm (0.1535 inches).
With respect to the color data provided in TABLE 5, the glass color in
terms of dominant wavelength and excitation purity was measured using
C.I.E. standard illuminant "C" with a 2° observer, following the
procedures established in ASTM E308-90. Glass color in terms of L*, a*
and b* was determined using the reference illuminant (D65) with a
10° observer.

[0048] Examples 1-3 and 5-12 have a solar factor of less than 30% and an
Lta in the range of greater than 0 and less than 5%. More particularly,
Examples 1-3, 6, 9 and 12 have an Lta in the range of greater than 0 and
less than 1%. As is now appreciated, these glasses will pass low
percentages of visible light. Examples 7 and 8 have an Lta in the range
of 1 to 2% and pass more visible light than Examples 1-3, 6, 9 and 12.
Examples 10 and 11 have an Lta in the range of 2-3% and pass more visible
light than Examples 7 and 8. Example 5 has an Lta of 4.5% and passes more
visible light than the examples 1-4 and 6-12. In the practice of the
invention, Examples 5, 7, 10 and 11 having an Lta in the range of 1.9 to
4.5, and a solar factor of equal to or less than 30% are preferred.

[0049] Example 4 has a solar factor of 38% which is greater than 30% and
does not meet the solar factor of equal to or less than 30% proposed by
CARB. It is believed the solar factor is greater than 30% because the Lta
is 20.43% and the TSET is 16,66%. It is believed that the high solar
factor and high Lta was a result of low additions of CoO (0.0319 wt %), a
low FeO (0.598 wt %) which resulted in low additions of the blue colorant
and low amounts of ferric sulfides.

[0050] As can be appreciated by those skilled in the art, when the dark
privacy glass of the invention is used as an automotive window, it is
preferably tempered and/or heat strengthened as know in the art to meet
automotive safety requirements.

[0051] Based on the description of the embodiments of the invention, it
can be appreciated that this invention is not limited to the particular
embodiments disclosed, but it is intended to cover modifications that are
within the spirit and scope of the invention, as defined by the appended
claims.